I don't think this line is correctly laid out [Obviously Ubuntu does not run on some processor architectures.]. Ubuntu runs on x86 processors, x86-64 processors, PowerPC processors and ARM (ARMv7 and up) SoC.
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Uri HerreraOct 25 '12 at 19:59

6 Answers
6

Lubuntu (Ubuntu with the LXDE desktop environment) or Xubuntu (Ubuntu with the Xfce desktop environment). Xubuntu is more "user friendly" -- more graphical tools for settings, better looking and better integrated applications and maybe better support (larger community). On the other hand, Lubuntu needs less RAM (Lubuntu about 128 MB, Xubuntu about 512 MB). It depends on your skills and preferences, you can try both and then choose.

to take into account: the default file manager pcmanfm do not support the trash-bin (or at least last time a tried lxde, some versions ago of ubuntu).
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enzotibJun 23 '11 at 14:19

+1 I would add that if you can handle not running a full desktop then I suggest using the fluxbox window manager. I don't have the exact numbers but it frees up even more precious RAM.
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KennyPeanutsJun 23 '11 at 15:52

Currently supported versions and their minimal requirements

The community wiki usually offers an up-to-date list of currently supported versions. Minimal system requirements for Ubuntu can be found there in the tech specs. Information on the derivatives is scarce but their requirements are less than what is listed here. Generally 32-bit versions take up less memory and tend to be faster on older systems, than their 64-bit counterparts. The Lists of Ubuntu certified hardware might also be of use to you.

Supported versions of Ubuntu

12.04, 14.04 and 14.10 Desktop

Ubuntu Desktop 11.04 and up uses Unity as the default GUI while the
previous releases used GNOME Panel by default. In order to run Unity
the system needs a more capable graphics adapter.

To install or try Xubuntu within the Desktop/Live CD, you need 512 MB
of memory and 5 GB of free space on your hard disk. Security and maintenance
updates will be provided for this release for 3 Years until April, 2017.

Supported versions of Lubuntu

14.04 ( Trusty Tahr )

A Pentium II or Celeron system with 128 MB of RAM and 5 GB of disk space for Lubuntu Desktop. Security and maintenance updates will be provided for this release for 3 Years until April, 2017.

Why you shouldn't use versions when their support has ended

Security risks: Eventually there will be an exploit that compromises security or system integrity of old Ubuntu versions

Software incompatibilities: Versions that are no longer supported will have increasing problems with this. Due to the lack of updates one will no longer be able to open the most recent LibreOffice documents or compile programs that need more recent libraries. Hardware drivers of recent devices will not be included in older kernels.

Decreasing availability of repositories: It might become very difficult to download software that does not already ship with the outdated version. Hosting repositories for very old versions cease to be economically viable at one point.

Xubuntu is designed to run on lightweight machines. I recently installed it on a machine with 768MB of RAM and other specs close to your machine and it runs without an issue.

Xubuntu is simply Ubuntu bundled with the Xfce Desktop Environment, a desktop environment designed to be fast and lightweight on lower end systems without compromising performance and visual style. Xubuntu 14.04 is a Long Term Support releases for which security and maintenance updates will be provided for 3 years until April, 2017.

Ubuntu is really slow (I can work properly with Unity 2D), Gnome Shell is also slow (plus for me Gnome Shell is awful in multitasking). KDE worked quite nice and I'm really impressed by it.

About which flavour to choose I can say this:

What do you want, better Looks or better Performance?

XFCE(Xubuntu) looks nicer and its environment has more
functionality, you can personalize it and change it in any way you want it (at
the cost of high memory use but still you need a good graphic card).

LXDE(Lubuntu) is faster overall but it lacks the looks.

I suggest to try Xubuntu and if it feels slower go for Lubuntu.

You can try Live-CDs to see how they look but you can test performance only after you installed them.

Have to say that even tough Linux system requirements are really low the desktop environment graphic requirements are high in my opinion.

Ubuntu MATE is a stable, easy-to-use operating system with a lightweight configurable desktop environment. The MATE Desktop has a rich history and is the continuation of the GNOME 2 desktop, which was the default desktop environment on many Linux and Unix operating systems for over a decade. Ubuntu MATE 15.04 will be an official Ubuntu release. Ubuntu MATE 15.04 is currently in beta, and will be released in April, 2015.